Additional Study Information: The purpose of this study is to determine if the study drugs, encorafenib, and cetuximab, taken in combination with pembrolizumab would improve compared to the outcome of pembrolizumab alone in study patients. Encorafenib and cetuximab target cancerous BRAF proteins and potentially slow down the growth of cancer cells. Pembrolizumab may help your immune system to kill cancer cells. Encorafenib is a BRAF inhibitor (a drug that can shrink or slow the growth of tumors) that is approved in several jurisdictions (including the United States US) in combination with cetuximab for the treatment of patients with metastatic BRAF mutant CRC, after prior therapy. Pembrolizumab is approved in the US for patients with mCRC with MSI-H/dMMR mutation that has not been treated.